Domenico Augustus Cesare Bertelli, A.C. Bertelli (or ‘Gus’ to his family and ‘Bert’ to his colleagues) was born in Italy and came to the UK as a four year old boy with his family in 1894. They settled in Cardiff and young ‘Gus’ was educated locally and apprenticed in the Cardiff steel works. He worked in the pattern and tool shops where his talent for engineering was quickly picked up. He did in fact return to Italy for a short while where he switched to the automotive industry, working at Fiat, during which time his interests turned towards motor engineering. During this period Bertelli had his first opportunity to experience motor racing, as riding mechanic for the great Felice Nazzaro, the pair winning the 1908 Targa Bologna.
By the time in 1926 when he had met Bill Renwick, who was to become his business partner, Bertelli had spent some time designing radial aero engines, and had designed and built the Enfield Allday ‘10/20’ and ‘10/25’ models for Allday and Onions. He was a regular motor racer, and had built his own racing car, ‘The Bertelli’, for Woolf Barnato (who later financed Bentley Motors). He was very well known in the motor trade, and at Brooklands, and was also deeply involved in the rapidly developing British motor industry. He had met and advised Herbert Austin when the ‘Austin 7’ was in its early design stage and was generally liked and respected within the industry.
William Renwick was also a talented engineer. His father had left him a small fortune and he had the funds to indulge his interest in all things mechanical. He had always aspired to build a high quality motor car and so with his design abilities and Bertelli’s experience and knowhow the two of them formed Renwick and Bertelli Ltd and set about producing what was to become the 1½ litre Aston Martin engine as a start to the new project.
Absolutely intrinsic to the development of the Aston Martin in the Bertelli era was the design and development of the four cylinder overhead cam 1½ litre engine. Using the Renwick patented wedge shaped combustion chamber, it was originally envisaged as an ‘off the shelf’ power unit to be offered throughout the motor industry, very much as the Gough or Meadows units powered a variety of cars. However, considerably developed over a ten year period and eventually with the capacity stretched to 2 litres, this engine powered all Aston Martins between 1927 and 1940.
Renwick and Bertelli’s first employee was a young draughtsman called Claude Hill, who was to be associated with Aston Martin up to and for some time after the Second World War. He drew the engine with a 69.25 mm bore and 99 mm stroke giving a capacity of 1492 cc. With a short and stiff cylinder block with plenty of waterways around the cylinders it had an oil thrower type rear main oil seal on the three main bearing balanced ‘Nitralloy’ crank, ‘Duralumin’ connecting rods with white metal bearings throughout and aluminium pistons. The cylinder head was to Renwick’s own patented design with a wedge shaped combustion chamber, the short valves being inclined at fourteen degrees with ⅜" diameter valve stems and collet type spring retainers with hardened caps and shims to take up the gross adjustment between the cam and the rockers. Fine adjustment was achieved by adjusting an eccentric mounting pin. The original engine, as fitted to the ‘T type’ had a single carburettor bolted mid way up the right hand side of the cylinder block. A large diameter internally cored port took the mixture up through the head gasket face and into the inlet manifold. This was fairly common practice at the time and very similar to a number of other small capacity engines, including the Bamford and Martin side-valve unit. The idea behind it was for the mixture to pass through the warm cylinder block to aid vapourisation of the fuel. However, it also warmed the mixture, making it less dense and therefore less useful. A simple aluminium cover over the ports produced the inlet manifold chamber. Later, this was developed into a rudimentary twin carburettor inlet manifold by mounting two one inch carburettors directly onto the cover. This made for a rather inefficient system and was always the Achilles’ heel of the engine.
The overhead cam was mounted on an aluminium carrier plate through which oil was fed to the rocker/cam interface, via holes in the cam lobes. The rocker pins were cantilevered off cast-in bosses on the carrier plate. This arrangement was functional but did not make for very consistent valve timing after adjustment and was not terribly strong. The cam was driven by a Reynolds inverted tooth chain with a blade type Weller tensioner spring, the drive taken from a Renwick and Bertelli patented Fabroil intermediate timing gear itself driven directly off the crank. The water pump, which pumped through the cylinder head only (the block being cooled by thermo syphon) was driven off a third gear on the dynamo shaft at the other end of which was a ‘Simms’ coupling which drove the magneto and gave vernier adjustment to enable accurate ignition timing.
Wet sump engines had a neat gear type oil pump driven off the intermediate gear countershaft, sucking up from the sump through an oil way in the front timing cover and pumping directly through another oil way into a side oil gallery. This was fitted with a mesh type filter, and from the gallery, three drillings took the oil down to the three main bearings. Oil feed to the cylinder head was taken from the gallery through a drilling via the cylinder head gasket (always a source of oil leaks) into the cam carrier plate and then through the front cam bearing and into the camshaft to feed the rocker/cam interface. A well built oil pump could produce well over 100 psi of pressure so it was regulated via a ball and spring type oil pressure relief valve, with the waste returning to the sump. The dry sump engines simply had a second (larger capacity) pump in tandem driven off a longer shaft. It pulled up oil from the sump, and pumped it into the oil tank, while what was the wet sump pressure pump now drew oil from the oil tank and pumped it into the oil gallery. This ‘dry sump’ system was more common in racing engines and very little used on production cars, mostly due to cost. It became one of the features of the pre-war Aston Martin distinguishing it from most other production sports car of the day and allowed Bertelli to boast about his competition developed engines to ‘racing specification’ with some validity.
The early clutches were a somewhat cumbersome pull off type. Later, by Borg and Beck and still heavy and slightly unwieldy, they were fitted with a simple drum brake to aid gear changes.
Although the Renwick and Bertelli engine was simple and had a relatively low compression at 6:1, it was the start of a line of engines, all closely related, which powered Aston Martin cars right up to 1940. The output increased from a lowly 50-55 bhp, to well over 100 bhp for the Speed Model engine of later 2 litre cars.